This invention relates to gas discharge displays and, more particularly, relates to gas discharge display devices for exhibiting analog signals in a bar graph from wherein the intensity can be increased or decreased according to the desired conditions of the surrounding environment.
An example of a prior art gas discharge bar graph display is set forth in U.S. Pat. No. 3,973,166 issued Aug. 3, 1976 to Thomas C. Maloney. This patent shows the structure of the bar graph having a plurality of cathode electrodes with each being a linear segment arranged in succession along a substrate of a sealed envelope to form the column that is to exhibit glow discharge. A single anode is placed adjacent the entire series of cathode segments and the operation of the anode controls the height of the glow discharge along the column of cathode segments. U.S. Pat. No. 3,967,158 issued on June 29, 1976 to Richard A. Saxon discloses circuitry for operating a bar graph having the structure set forth in the above cited Maloney patent.
There are several disadvantages to the existing types of gas discharge display bar graphs. The primary disadvantage centers on the fact that these prior bar graphs do not have the ability to adjust the intensity of the glow discharge especially with respect to increasing the intensity to provide adequate contrast to a generally bright ambient environment. The most common example of such a situation is with respect to aircraft cockpit instrumentation where the aircraft operates in a range of varying conditions from direct sunlight to near total darkness. Obviously, when operating in direct sunlight it is necessary to have the intensity of the bar graph increased sufficiently to provide the satisfactory contrast, so that the magnitude of the bar graph can easily be detected by the pilot. The present technology limits the intensity of a gas discharge display to approximately 10,000 foot lamberts peak brightness. The ability to increase the intensity of the light cannot be accomplished by increasing the current, because the technical limits of the present art gas displays do not permit increased current to exceed the 10,000 foot lamberts intensity without sacrificing the life or integrity of the display.
In other situations where the aircraft is operating in total darkness, the brightness of the bar graph should be reduced considerably in accordance with the dark surroundings to avoid discomfort to the pilot's eyes. It is necessary to dim the cockpit instrumentation to eliminate the loss of so-called "night vision" of the pilot.